Coronary artery disease (CAD) is the major cause of death in Type 2 diabetic and metabolic syndrome patients (i.e., patients that fall within the ‘deadly quartet’ category of impaired glucose tolerance, insulin resistance, hypertriglyceridaemia and/or obesity).
The hypolipidaemic fibrates and antidiabetic thiazolidinediones separately display moderately effective triglyceride-lowering activities, although they are neither potent nor efficacious enough to be a single therapy of choice for the dyslipidaemia often observed in Type 2 diabetic or metabolic syndrome patients. The thiazolidinediones also potently lower circulating glucose levels of Type 2 diabetic animal models and humans. However, the fibrate class of compounds are without beneficial effects on glycaemia. Studies on the molecular actions of these compounds indicate that thiazolidinediones and fibrates exert their action by activating distinct transcription factors of the peroxisome proliferator activated receptor (PPAR) family, resulting in increased and decreased expression of specific enzymes and apolipoproteins respectively, both key-players in regulation of plasma triglyceride content.
PPAR-δ activation was initially reported not to be involved in modulation of glucose or triglyceride levels. (Berger et al., J. Biol. Chem. 1999, 274, 6718-6725). Later it was shown that PPAR-δ activation leads to increased levels of HDL cholesterol in db/db mice (Leibowitz et al., FEBS letters 2000, 473, 333-336). Further, a PPAR-δ agonist when dosed to insulin-resistant middle-aged obese rhesus monkeys caused a dramatic dose-dependent rise in serum HDL cholesterol while lowering the levels of small dense LDL, fasting triglycerides and fasting insulin (Oliver et al., PNAS 2001, 98, 5306-5311). The same paper also showed that PPAR-δ activation increased the reverse cholesterol transporter ATP-binding cassette A1 and induced apolipoprotein A1-specific cholesterol efflux. The involvement of PPAR-δ in fatty acid oxidation in muscles was further substantiated in PPAR-α knock-out mice. Muoio et al. (J. Biol. Chem. 2002, 277, 26089-26097) showed that the high levels of PPAR-δ in skeletal muscle can compensate for deficiency in PPAR-α. In addition to the effects on cholesterol homeostasis, PPARδ treatment was observed to lower plasma glucose and insulin and improve insulin sensitivity in diabetic ob/ob and db/db mice and high fat diet induced insulin resistant mice (PNAS 2003, 100, 15924-15929; PNAS 2006, 103, 3444-3449). Taken together these observations suggest that PPAR-δ activation is useful in the treatment and prevention of Type 2 diabetes, cardiovascular diseases and conditions including atherosclerosis, hypertriglyceridemia, and mixed dyslipidaemia (WO 01/00603).
A number of PPAR-δ compounds have been reported to be useful in the treatment of hyperglycemia, hyperlipidemia and hypercholesterolemia (WO 02/59098, WO 01/603, WO 01/25181, WO 02/14291, WO 01/79197, WO 99/4815, WO 97/28149, WO 98/27974, WO 97/28115, WO 97/27857, WO 97/28137, and WO 97/27847). WO 2004093879, WO 2004092117, WO 2004080947, WO 2004080943, WO 2004073606, WO 2004063166, WO 2004063165, WO 2003072100, WO 2004060871, WO 2004005253, WO 2003097607, WO 2003035603, WO 2004000315, WO 2004000762, WO 2003074495, WO 2002070011, WO 2003084916, US 20040209936, WO 2003074050, WO 2003074051, WO 2003074052, JP 2003171275, WO 2003033493, WO 2003016291, WO 2002076957, WO 2002046154, WO 2002014291, WO 2001079197, WO 2003024395, WO 2002059098, WO 2002062774, WO 2002050048, WO 2002028434, WO 2001000603, WO 2001060807, WO 9728149, WO 2001034200, WO 9904815, WO 200125226, WO 2005097098; WO 2005097762; WO 2005097763.
Glucose lowering as a single approach does not overcome the macrovascular complications associated with Type 2 diabetes and metabolic syndrome. Novel treatments of Type 2 diabetes and metabolic syndrome must therefore aim at lowering both the overt hypertriglyceridaemia associated with these syndromes as well as alleviation of hyperglycaemia. This indicates that research for compounds displaying various degree of PPAR-δ activation should lead to the discovery of efficacious triglyceride and/or cholesterol and/or glucose lowering drugs that have great potential in the treatment of diseases such as type 2 diabetes, dyslipidemia, syndrome X (including the metabolic syndrome, i.e., impaired glucose tolerance, insulin resistance, hypertrigyceridaemia and/or obesity), cardiovascular diseases (including atherosclerosis) and hypercholesteremia.